1. Field of the Invention
The present invention relates to a fixing unit and an image-forming apparatus having the same. More particularly, the present invention relates to a fixing unit having pressure rollers and an image-forming apparatus having the same.
2. Description of the Related Art
Generally, an image-forming apparatus is a device that prints an image on paper, which is a printing medium. An electrophotographic image-forming apparatus, which is a type of image-forming apparatus, includes a light-scanning unit that scans an optical signal that corresponds to an image desired to be printed on a photosensitive medium, a developing unit that supplies toner to an electrostatic latent image formed on the photosensitive medium to develop the latent image into a visual image, and a fixing unit that fixes the visual image on paper. An inkjet image-forming apparatus, which is another kind of image-forming apparatus, also tends to have a fixing unit that quickly fixes ejected ink on paper.
FIGS. 1 and 2 are sectional views of conventional fixing units.
Referring to FIG. 1, a fixing unit 10 according to a first embodiment of a conventional fixing unit includes a heat roller 11 having a heat source 12 therein to generate heat, and a pressure roller 13 closely attached to the heat roller 11 with a fixing nip N interposed. Because the fixing performance of the fixing unit is proportional to the area of the fixing nip, the diameter of the pressure roller 13 should be made large to improve the fixing performance of the fixing unit 10 having one pressure roller 13. Accordingly, it is difficult to manufacture a small-sized image-forming apparatus (not shown).
Referring to FIG. 2, a fixing unit 20 according to a second embodiment of a conventional fixing unit includes a heat roller 21 having a heat source 22 therein to generate heat, and first and second pressure rollers 23 and 25 closely attached to the heat roller 21 with the first and second fixing nips N1 and N2 interposed, respectively. Though small, the fixing unit 20 has a fixing nip of an increased area and thus improved fixing performance is expected. However, the front end of a paper that has passed through the first fixing nip N1 does not pass through the second fixing nip N2 but is caught in the second pressure roller 25, so that paper jams frequently occur, which deteriorates the reliability of the paper transfer.
Accordingly, a need exists for an image forming apparatus having an improved fixing unit that increases the reliability of paper transfer through the fixing unit by substantially preventing the occurrence of paper jams.